1. Field of the Invention
The present invention generally relates to recording media and information storage apparatuses, and, more particularly, to a recording medium and an information storage apparatus which allocate an ID to each piece of data and store information.
In recent years, there has been an increasing demand for larger capacity information storage apparatuses, as the amount of information in the field of information processing has been increasing rapidly. In a recording medium, such as a magneto-optical disk, used in an information storage apparatus, information is recorded based on IDs. Because of this ID-based recording method, a larger recording capacity at higher recording density requires a larger number of IDs, resulting in poor formatting efficiency.
In a magneto-optical disk, headers including IDs are formed by pits. A disk substrate is produced by an injection molding method using a base plate. On the base plate, the pits are already formed by a photo processing technique. On the disk substrate, a recording layer and a protection layer are formed to produce the magneto-optical disk. Thus, the pit size is determined by the wavelength of the laser beam.
In the magneto-optical disk, the mark size is reduced by the MSR (Magnetically induced Super Resolution) technology to a point where the pre-formatted pit size is twice or three times larger than the recorded mark size. As a result, the existence of the pits hinders the improvement in recording density.
2. Description of the Related Art
FIG. 1 shows an example format of a conventional magneto-optical disk.
A magneto-optical disk 1 of the prior art is rotated at a constant rotational speed. The relative speed between a light beam and the magneto-optical disk 1 on the inner peripheral side of the magneto-optical disk 1 is different from that on the outer peripheral side of the magneto-optical disk 1. Therefore, the magneto-optical disk 1 is divided into four zones Z1 to Z4. The innermost zone Z1 has the lowest recording frequency among the four zones Z1 to Z4, and the outermost zone Z4 has the highest recording frequency. This setting of recording frequencies is called a ZCAV (Zone Constant Angular Velocity) method, which is used to improve recording capacity.
In the magneto-optical disk 1, a header area 2 is formed in every sector having a predetermined length. A light beam is positioned to a target sector in accordance with address (ID) information recorded in advance on the corresponding header area 2 with a pit. A data area 3 in which information is to be stored is formed between every two header areas 2.
FIG. 2 shows the data structure of an example data track of the conventional magneto-optical disk.
The data track is made up of a plurality of data sectors 4. Each of the data sectors 4 includes a header 5 and a data field 6. An address for identifying each data field 6 is stored in each corresponding header 5, and information is stored in each data field 6.
A buffer 7 is disposed between every two data sectors 4. A gap 8 is formed between a header 5 and a data field 6. In each of the zones Z1 to Z4, the headers 5 of two adjacent tracks are situated next to each other. The data fields 6 of two adjacent tracks in the same zone are also situated next to each other.
FIG. 3 shows the data structure of an example header of the conventional magneto-optical disk.
Each of the headers 5 comprises a sector mark 9, a first VFO (Variable Frequency Oscillator) synchronizing area 10, an address mark 11, a first track address 12, a first sector address 13, a first error correcting code 14, a second VFO synchronizing area 15, an address mark 16, a second track address 17, a second sector address 18, a second error correcting code 19, and a postamble 20.
The sector mark 9 represents the start of a data sector 4. The first VFO synchronizing area 10 initiates VFO synchronization for reading the first track address 12 and the first sector address 13. The first address mark 11 represents the start of the first track address 12 and the first sector address 13. The first track address 12 represents the track address of scanned data. The first sector address 13 represents the sector address of the scanned data. The first error correcting code 14 is used to correct an error in the first track address 12 and the first sector address 13.
The second VFO synchronizing area 15 initiates VFO synchronization for reading the second track address 17 and the second sector address 18. The second address mark 16 represents the start of the track address 17 and the second sector address 18. The second track address 17 represents the track address of scanned data. The second sector address 18 represents the sector address of the scanned data. The second error correcting code 19 is used to correct an error in the second track address 17 and the second sector address 18. The postamble 20 represents the end of the header 5.
The position of a light beam is determined from either the combination of the first track address 12 and the first sector address 13 or the combination of the second track address 17 and the second sector address 18.
FIG. 4 shows the data structure of an example data field of the conventional magneto-optical disk.
The data field 6 comprises a third VFO synchronizing field 21, a synchronizing signal field 22, a data storage field 23, an error correcting code field 24, and a postamble field 25.
The third VFO synchronizing area 21 initiates VFO synchronization for recording and reproducing data. The synchronizing signal field 22 is synchronizing with the data field 6, and initiates synchronization for reproducing data. The data storage field 23 stores data. The error correcting code field 24 is used to detect and correct an error in the data stored in the data storage field 23. The postamble field 25 is added to reproduce the end of the data.
As explained above, the conventional magneto-optical disk 1 has a header 5 in each data sector 4 to determine the position of a light beam.
However, despite the small size of marks formed by the MSR technology, the headers are formed by pits that are twice or three times larger than the marks, because the pits are read out without the MSR technology. The pit size is restricted to the size corresponding to the wavelength of the laser beam. If the data density is doubled or tripled by the MSR technology, a large proportion of the recording area is occupied by the headers. As a whole, the recording density cannot be improved due to the large-sized pits. Furthermore, since one header is provided for each sector in the conventional magneto-optical disk, the formatting efficiency cannot be improved. Also, stagger caused in land/groove tracks reduces the formatting efficiency.